1. Field of the Invention
The present invention relates to a target recognition apparatus. The invention particularly relates to a target recognition apparatus that measures a distance from a vehicle to a target, based on parallax information from two images of the target simultaneously picked up by two cameras (a left camera and a right camera) that are mounted on the vehicle, with a predetermined distance between the cameras in a horizontal direction.
2. Description of the Related Art
Conventionally, there has been known a target recognition apparatus that measures a distance from a vehicle to a target, based on parallax information from of target images picked up by two cameras that are mounted on the vehicle at positions at the same height above ground level, with a predetermined distance between the cameras. Generally, this kind of target recognition apparatus generates edge images by carrying out an edge extraction processing to an input left image that is input after the left camera has picked up this image, and an input right image that is input after the right camera has picked up this image. The target recognition apparatus measures a distance to the target, based on a parallax between the corresponding edge positions in the two edge images.
A filter that passes only vertical components of the photographed images is used as an edge extracting filter that carries out an edge extraction processing of the photographed images. Therefore, when a vehicle has an angular shape, it is easy to extract both end portions of the vehicle as edges. However, when a vehicle has a curved surface on the side surface and has a relatively round cross-sectional shape, it is difficult to detect vertical components, and thus, it is difficult to extract edges.
Further, when cameras that can pick up images of a wide-angular range are used, a photographed vehicle appears to have a round shape even if the vehicle has actually an angular shape with many vertical components. This is due to a distorted astigmatism. Therefore, it becomes difficult to extract edges. As explained above, when a target that has curves at both end portions is photographed, edges at the ends of the target do not always appear on the photograph, even if the edge extraction processing is carried out on the photographed target. Therefore, it is not easy to specify both ends of the target, that is, a width of the target.